Rotary mechanism having apex seals with low contact pressure

ABSTRACT

A rotary mechanism of trochoidal type, having means for limiting the gas pressure under the apex seals which urges the seals radially outwardly against the trochoidal running surface. Excessive outward pressure results in undue wear of the seals and the trochoidal surface, and in this invention the underseal gas pressure is restricted by a seal assembly which is responsive to chamber pressures of the engine.

United States Patent 1191 Pratt Aug. 12, 1975 [54] ROTARY MECHANISMHAVING APEX 3,253,581 5/1966 Nallinger 418/113 SEALS WITH LOW CONTACTPRESSURE 3,369,528 2/1968 lrgens 418/61 A 3,551,080 12/1970 Feller418/61 A 1 lnventorl Winthrop Pratt, North Haledon, 3,794,450 2/1974Klomp 418/122 NJ. [73] Assignee: Curtiss-Wright Corporation, PrimaryExaminerc Husar wood Ridge, Ni Attorney, Agent, or firm-Raymond P.Wallace;

Victor D. Behn [22] Filed: May 13, 1974 [21] Appl. No.: 469,594 [57]ABSTRACT A rotary mechanism of trochoidal type, having means 52 US. Cl.418/113; 418/123- 418/61 A for limiting the gas Pressure under the apexseals 51 Int. c1. FOIC 19/02 which urges the Seals radially outwardlyageingt the [58] Field of Search 418/111 122 123 61 A trochoidal runningsurface. Excessive outward pressure results in undue wear of the sealsand the trochoi- [56] References Cited dal surface, and in thisinvention the undersea] gas pressure is restricted by a seal assemblywhich is re- UNITED STATES PATENTS sponsive to chamber pressures of theengine. 3.03.3,180 5/1962 Bentele 418/123 3,127,095 3/1964 Froede418/122 8 m 6 Drawing g r is 32 1O 32 31c. s4 19 to BACKGROUND OF THEINVENTION This invention relates to rotary mechanisms of trochoidal typehaving a multi-apexed rotor with a sealing strip at each apex thereofsweeping a sealing surface, and more particularly to means for reducingand controlling the gas pressure under the apex seals.

In rotary mechanisms of the trochoidal type each apex of the rotor has aslot of appropriate radial depth and extending from side to side of therotor in the longitudinal direction parallel to the axis of rotation. Ineach such slot is disposed a seal strip with one edge presentedgenerally radially to the inner trochoidal surface of the peripheralhousing shell, the other edge being retained in the slot with a springbetween the inner edge and slot bottom urging the seal strip radiallyoutwardly. Because of necessary clearance between the seal strip and thewalls of its slot, gas pressure from the operating chamber on one sideor the other of the seal enters the slot, and acting on the inner edgeof the seal also urges it outwardly.

During the larger part of the seal travel along the trochoidal surface,centrifugal forces also urge the seals radially outwardly. However, whenthe seal is moving in the region of the cusps of the trochoid thedirection of centrifugal force reverses and tends to urge the sealinwardly. The combined forces of spring pressure and gas pressure underthe seal must be sufficient to oppose the inward urging of centrifugalforce and hold the seal in contact with the trochoidal surface.Therefore, at such times as centrifugal force is outwardly directed thetotal force exerted on the seals may be excessively large, which causesrapid wear of the seals themselves and also of the trochoidal shellsurface.

Various expedients have been suggested in the prior art to control theoutward thrust of the apex seals, such as systems of flyweights andcounterbalancing responsive to centrifugal throw, which are intended torestrain or retract the apex seals from outward movement as outwardcentrifugal thrust increases. However, the seal strips are small andvery light in weight in comparison to the other parts of the mechanism,and such counterbalancing systems require a number of parts which aredelicate, require precise calculation and manufacture, are difficult toadjust, and very expensive to produce and assemble. The presentinvention overcomes these prior art difficulties of multiple parts,delicacy of manufacture, and expensive production and assembly.

SUMMARY This invention provides a rotary mechanism of trochoidal typewherein the sealing means is responsive to pressure in the operatingchambers to restrict and control the gas pressure under the apex sealsto a moderate amount sufficient for good sealing action. The seal assembly at each rotor apex is constructed to react to the higher chamberpressure on either side of the sea] as it alternates in operation,closing the clearance between the seal and its slot and channeling asmall amount of high pressure gas to the under side of the seal.

It is an object of this invention to provide a rotary Combustion enginehaving improved sealing means.

It is another object to provide such an engine in which the apex sealshave low contact pressure against the running surface of the peripheralhousing.

A further object is to provide apex sealing means responsive to gaspressures in the operating chambers to restrict and control sealpressure against the peripheral shell.

Other objects and advantages will become apparent on reading thefollowing specification in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of a two-lobed rotarymechanism with one side plate removed;

FIG. 2 is an enlarged view of the apex sealing means;

FIG. 3 is a fragmentary section taken on line 3-3 of FIG. 2;

FIG. 4 is an enlarged cross-section taken on line 44 of FIG. 1',

FIG. 5 is a perspective view of a portion of the apex sealing means; and

FIG. 6 is a similar view of a modification of the device shown in FIG.5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will be describedprincipally in terms of a rotary internal combustion engine, but it isto be understood that it is equally applicable to such other trochoidalmechanisms as expansion engines, pumps, and compressors.

In FIGS. 1 and 4 there is shown a rotary combustion engine 11 having aperipheral housing shell 12 with a multi-lobed generally trochoidalinner surface 13; although shown with two lobes, the shell 12 may haveany number of lobes. The shell is closed by a pair of side plates 14, ofwhich only the rearmost is shown in FIG. 1. A shaft 16 is journaled bythe side walls coaxial with the shell and has an eccentric portion 17within the housing, on which is rotatably mounted a rotor 18 whichdefines with the housing a plurality of operating chambers 19 ofvariable volume.

As shown, the rotor 18 has three apex portions 21, but the number ofapex portions will vary in accordance with the number of lobes of theepitrochoid; that is, the rotor will have one more apex portion then thenumber of lobes of the peripheral shell, two apex portions for a singlelobe, four apex portions for three lobes, etc. Each apex portion carriessealing means 22 which effects sealing between the rotor apexes and theinner trochoidal surface 13 of the shell, and serves to keep thechambers 19 separate from each other. Gas sealing between the sides ofthe rotor and the side walls 14 is provided by side seals 10 carried ingrooves on the sides of the rotor and near the periphery thereof. Atleast one oil seal ring 15 is carried by the rotor radially inward fromthe side gas seals.

Inlet port means is provided, which may be either the peripheral port 23through the shell, or the side port 24 through one or both side walls,or any combination of such. Outlet port means 26 is also provided, whichmay be through any of the housing walls. The angular location, size, andshape of such ports may vary according to the design of the particularmechanism. When the device is a combination engine, ignition means orfuel injection means indicated by the lightning arrow 27 is provided inthe compression region, generally opposite to the inlet and outletregion.

The apex sealing means 22 is shown much enlarged in FIG. 2, andpositioned in its operating environment in FIG. 4. Each apex portion 21of the rotor has acylindrical bore 28 therethrough in the axialdirection from one side to the other of the rotor. A seal slot 29 in therotor apex communicates with bore 28 and extends radially therefrom tothe rotor apex, the seal slot 29 also extending axially the full widthof the rotor. Disposed within bore 28 are a plurality of elements whichcollectively comprise a multipart generally cylindrical seal pin 31(best shown in FIG.

The composite seal pin 31 is divided longitudinally and transversely,resulting in the four parts 31a, 31b, 31c, and 31d shown in FIG. 5. Thediameter of the seal pin is slightly less than the diameter of the bore28 in which it is disposed. Considered as a whole, the multipart sealpin 31 has an axial slot 32 of the same transverse width as slot 29 inthe rotor apex, and receiving the radially inward edge of apex sealstrip 33, which extends further outwardly in the radial directionthrough slot 29 and makes sliding contact with the trochoidal innersurface 13. A spring 34 is positioned in the seal pin slot 32 under theseal strip 33 to urge it radially outwardly. The longitudinal divisionof the seal pin 31 is along the median plane of slot 32, so that whenthe pin is positioned within its bore with the two sides of its slotparallel, the bottom of slot 32 is closed and flat. In effect, when theelements of the sealing system are assembled in the rotor apex, slot 29in the rotor and slot 32 in the seal pin comprise a single apex sealslot.

The conditions of the operating cycle of a trochoidal mechanism are suchthat pressures on opposite sides of an apex seal differ according towhich portion of the cycle is being performed in the adjacent chambers.In a combustion engine, at the rotor position shown in FIG. 1 thechamber 19 at the top of the illustration has just fired, and thepressure therein is high. The chamber on the lefthand side is intakingfresh fuel and air mixture, and its pressure is therefore low. Therighthand chamber is exhausting, and although open to atmosphere itspressure is still higher than that of the lefthand chamber, but lowerthan that of the chamber which is undergoing combustion.

For reasons of manufacturing tolerances and to accommodate thermalchanges of dimension, the thickness of the apex seals is less than thewidth of their slots, so that they fit therein with a certain degree oflooseness. Therefore the seals travel transversely from side to side oftheir slots toward the sides having lower pressure, and gas from thehigh pressure side can enter the rotor slot. Although in the prior artthis high pressure gas entering the seal slot has been allowed topermeate under the seals and add its pressure to the radially outwardurging of the springs, as set forth above this additional undersealpressure can sometimes be undesirable.

FIG. 2 shows the operation of the sealing means of this invention incontrolling and limiting this underseal gas pressure. As shown, the highpressure chamber is at the right side of the figure. Because thediameter of pin 31 is less than that of its bore, gas pressure acts onthe outer cylindrical surface of the pin and the half of the pin on thehigh pressure side rolls or tilts slightly within the bore so that theradially outer edge 36 of that half of the pin formed by parts 31a and31b tips against the plane face of apex seal 33 and prevents gaspressure from traveling inwardly along the side of the apex seal. In theoperation of the mechanism, when the other side of the apex seal becomesthe high pressure chamber in the next following portion of the cycle,the seal travels laterally across its slot and the corollary motion ofthe other half of the sealing pin, formed by parts 31c and 31d, occurs.

As is shown in FIGS. 4 and 5, pin 31 is divided transversely aboutmidway of its length. In the gap 37 thus formed between the two endportions a generally horseshoe-shaped wave spring 38 is disposed, urgingthe two end portions axially outwardly against the side walls. Theclearances shown in the drawings have been exaggerated for clarity ofillustration. Through this gas 37 a small amount of high pressure gasbleeds into the underseal space to assist spring 34 in holding the apexseal against the trochoidal surface. The rollling motion of the tiltedportion of pin 31 within its cylindrical bore is such that the bottom ofthe slot in the pin does not separate between right and left halves, butremains closed along the dividing line by the corner of the shoulder.

In order that the gas under the seal shall not build up to anundesirably high pressure a relief vent is provided. On at least one endface of pin 31 the corners of the bottom shoulder are chamfered orgrooved at 39 along the radial dividing surfaces. The axial width of therotor 18 is slightly less than the axial spacing between side walls 14(best seen in FIG. 4) in order to provide suitable running clearances.There is thus a space 41 at each side of the rotor between the side gasseals 10 and the oil seal 15, so that the underseal gas bleeds throughvent 39 into space 41. The relief groove 39 in the end face of the pinis axially a little deeper (shown in FIG. 3) than the nominal axialdepth of space 41, so that even if the rotor should run more to one sideor the other the underseal space remains in communication with space 41.Ordinarily a slight hub, thrust bearing, or other means (not shown) isprovided to prevent the rotor from bearing directly against side walls14. If desired, a vent 39 may be provided at each end face of pin 31.

The cross-sectional area of the vent means 39 is sized in proportion tothe cross-section of gap 37 so that the underseal gas pressure shall notbleed off too rapidly and will always exert the desired amount ofradially outward thrust against the apex seals, according to the designof the mechanism. Spaces 41 at the rotor sides are periodically ventedto one of the ports, or by other convenient means.

In some engines or other trochoidal mechanisms, owing to small size ofthe parts or the presence of oil around the pins or to other factors,gas pressure may not readily enter the top portion of bore 28 to causethe high pressure side of the pin to tilt and press its sealing edge 36against the apex seal. For this condition there is provided themodification of the seal pin shown in FIG. 6.

Seal pin 51 is formed of four parts, similar to those of the previouslydescribed embodiment, of which 51a and 510 are shown in FIG. 6. The topedges of each side are flatted off at 52 so that the sealing edges 36are radially a little further inward than in pin 31. In the topquadrants of each side of the pin, grooves 53 are provided on itsexternal diameter, running out at the cylindrical surface at one end anddebouching into the flats 52 at the other end without interrupting thesealing edges 36. These grooves 53 provide gas entry to the externalsurface of the pin and allow the halves to tilt at appropriate portionsof the cycle to present sealing edges 36 to the plane surfaces of theapex seals. The depth of grooves 53 need by only slight, and theirnumber is not critical, although it is preferred that there be at leasttwo such grooves in each piece of pin 51. If convenient, the gas-entrygrooves 53 may be formed in the inner surface of bore 28 instead of onthe sealing pin.

As shown in the present mechanism the side gas seals have their trailingends butted against the circumference of the seal pin on its leadingside. The leading ends of the side seals rest on shoulders 54 formed inthe ends of the trailing halves of the seal pins. However, the mechanismmay be designed to have both ends of the side gas seals butt against thepins, or both ends of the side seals resting on such shoulders. Ineither of the latter cases the leading and trailing halves of the sealpins are mirror images of each other.

Various elements of such trochoidal rotary mechanisms have been omittedfrom the drawings as not necessary to an understanding of the invention.Examples of such omissions are phasing gears for maintainingregistration of the rotor within the housing lobes, certain bearings,passages within the rotor and the housing for cooling, and similarelements.

It will be apparent from the foregoing description that the presentinvention provides a trochoidal mechanism having apex sealing meanswhich is automatically responsive to gas pressures within the operatingchambers, restricting and controlling the amount of high pressure gasadmitted to the underside of the apex seals and preventing build-up ofhigh underseal pressures. Excessive wear of the apex seals and of thetrochoidal running surface are thus prevented, and power is saved byreducing the high friction which would otherwise occur.

What is claimed is:

1. A rotary mechanism having a housing comprising a peripheral shellhaving an inner surface and a pair of side walls defining therein arotor cavity, a shaft journaled by the side walls coaxially with theperipheral shell and having an eccentric portion within the cavity, arotor having a plurality of apex portions and rotatably mounted on theshaft eccentric portion and defining with the housing a plurality ofoperating chambers of variable volume wherein gas pressure alternatesbetween lower and higher pressures, wherein the improvement comprises:

a. each rotor apex portion having a radially disposed slot extending inthe axial direction from one side of the rotor to the other;

b. a seal strip disposed within the slot and radially movable thereinand sweeping the inner surface of the shell in sealing relation, therebeing an underseal space between the radially inner edge of the sealstrip and the bottom of the slot;

0. each rotor apex portion having associated sealing means responsive togas pressure to restrict entry of gas into the underseal slot spaceradially inward of the seal strip;

d. the associated sealing means comprising movable means disposed oneach side of the apex seal strip and extending in the axial directionand of substantially the same length as the apex seal strip, eachmovable means having a sealing edge facing the apex seal strip andparallel therewith, the movable means on the side exposed to theoperating chamber having higher pressure being responsive to gaspressure in said chamber to appose its sealing edge to the side of theapex seal strip to occlude the underseal space from entry of gas.

2. The combination recited in claim 1, wherein the sealing edge of themovable means is interrupted for a portion of its length to provide achannel for entry of a small amount of gas into the underseal space toprovide underseal pressure urging the seal radially outwardly.

3. The combination recited in claim 2, wherein the underseal space isvented to prevent build-up of high pressure therein.

4. The combination recited in claim 1, wherein each apex portion has abore therethrough from one side of the rotor to the other communicatingwith the slot in the rotor apex and radially inward therefrom, and theassociated movable means comprises a multipart generally cylindrical pindisposed within the bore, the pin having in its radially outer portion aslot congruent with the rotor slot and receiving the radially inner edgeof the apex seal and defining therewith the underseal space, the pinbeing divided into a leading half and a trailing half with the outermostedge of the slot portion in each half comprising the sealing edge, thehalf pin exposed to the chamber of higher pressure rotating within thebore in response to such pressure on its outer surface to appose itssealing edge to the leading face of the apex seal.

5. The combination recited in claim 4, wherein the generally cylindricalpin is divided across its diameter approximately midway between itsends, and a spring member is disposed between the two end portionsurging them axially apart to form a midseal gap therebetween, themidseal gap forming an interruption of the sealing edges of the leadinghalf and the trailing half for entry of gas from the chamber of higherpressure into the underseal space to urge the apex seal radiallyoutwardly.

6. The combination recited in claim 5, wherein the axially outer face ofat least one end portion of the generally cylindrical pin has a groovetherein communicating with the underseal space to vent gas therefrom.

7. The combination recited in claim 4, wherein the multipart generallycylindrical pin has a plurality of gas-entry grooves formed in theradially outermost quadrant of the outer surface of the leading half andthe trailing half to allow gas in the chamber of higher pressure to acton the outer surface of the pin to rotate it toward the seal.

8. The combination recited in claim 7, wherein a flat surface is formedon the radially outermost portions of the leading half and the trailinghalf of the multipart pin, and the gas-entry grooves have their orificesdebouching in the flat surface without interrupting the sealing edges.

1. A rotary mechanism having a housing comprising a peripheral shellhaving an inner surface and a pair of side walls defining therein arotor cavity, a shaft journaled by the side walls coaxially with theperipheral shell and having an eccentric portion within the cavity, arotor having a plurality of apex portions and rotatably mounted on theshaft eccentric portion and defining with the housing a plurality ofoperating chambers of variable volume wherein gas pressure alternatesbetween lower and higher pressures, wherein the improvement comprises:a. each rotor apex portion having a radially disposed slot extending inthe axial direction from one side of the rotor to the other; b. a sealstrip disposed within the slot and radially movable therein and sweepingthe inner surface of the shell in sealing relation, there being anunderseal space between the radially inner edge of the seal strip andthe bottom of the slot; c. each rotor apex portion having associatedsealing means responsive to gas pressure to restrict entry of gas intothe underseal slot space radially inward of the seal strip; d. theassociated sealing means comprising movable means disposed on each sideof the apex seal strip and extending in the axial direction and ofsubstantially the same length as the apex seal strip, each movable meanshaving a sealing edge facing the apex seal strip and parallel therewith,the movable means on the side exposed to the operating chamber havinghigher pressure being responsive to gas pressure in said chamber toappose its sealing edge to the side of the apex seal strip to occludethe underseal space from entry of gas.
 2. The combination recited inclaim 1, wherein the sealing edge of the movable means is interruptedfor a portion of its length to provide a channel for entry of a smallamount of gas into the underseal space to provide underseal pressureurging the seal radially outwardly.
 3. The combination recited in claim2, wherein the underseal space is vented to prevent build-up of highpressure therein.
 4. The combination recited in claim 1, wherein eachapex portion has a bore therethrough from one side of the rotor to theother communicating with the slot in the rotor apex and radially inwardtherefrom, and the associated movable means comprises a multipartgenerally cylindrical pin disposed within the bore, the pin having inits radially outer portion a slot congruent with the rotor slot andreceiving the radially inner edge of the apex seal and definingtherewith the underseal space, the pin being divided into a leading halfand a trailing half with the outermost edge of the slot portion in eachhalf comprising the sealing edge, the half pin exposed to the chamber ofhigher pressure rotating within the bore in response to such pressure onits outer surface to appose its sealing edge to the leading face of theapex seal.
 5. The combination recited in claim 4, wherein the generallycylindrical pin is divided across its diameter approximately midwaybetween its ends, and a spring member is disposed between the two endportions urging them axially apart to form a midseal gap therebetween,the midseal gap forming an interruption of the sealing edges of theleading half and the trailing half for entry of gas from the chamber ofhigher pressure into the underseal space to urge the apex seal radiallyoutwardly.
 6. The combination recited in claim 5, wherein the axiallyouter face of at least one end portion of the generally cylindrical pinhas a groove therein comMunicating with the underseal space to vent gastherefrom.
 7. The combination recited in claim 4, wherein the multipartgenerally cylindrical pin has a plurality of gas-entry grooves formed inthe radially outermost quadrant of the outer surface of the leading halfand the trailing half to allow gas in the chamber of higher pressure toact on the outer surface of the pin to rotate it toward the seal.
 8. Thecombination recited in claim 7, wherein a flat surface is formed on theradially outermost portions of the leading half and the trailing half ofthe multipart pin, and the gas-entry grooves have their orificesdebouching in the flat surface without interrupting the sealing edges.